This invention relates to elements for use in audio equipment, and particularly to acoustic vibratory elements such as diaphragms for speakers and microphones and cartridge cantilevers for record players, the elements being lightweight, highly stiff and highly elastic and having a sufficient internal loss (damping) and an improved temperature resistance.
In general, acoustic vibratory elements such as acoustic diaphragms and cantilevers are required to have low density, high stiffness, high elasticity, and sufficient internal loss. Low density, high stiffness and high elasticity are necessary to provide efficient reproduction up to a high frequency range without causing partial vibration while sufficient internal loss (damping) is effective for preventing sound pressure from rapidly rising at about resonance frequencies in the high range as well as improving damping characteristics. Acoustic vibratory elements are known which are formed from lightweight, highly elastic materials, for example, metals such as aluminum, titanium and beryllium, and composite materials such as carbon filter reinforced plastics (CFRP). None of these known materials are free of the problem of poor internal loss. Acoustic diaphragms with sufficient internal loss are also known which are formed from paper, synthetic resins or composite materials thereof. Though these materials have sufficient internal loss, they show a low modulus of elasticity and hence, a low specific modulus (ratio of modulus of elasticity E to density .rho., simply referred to as "E/.rho."). There is a need for material which has not only a low density and high elasticity, but also sufficient internal loss.
Recently, the inventors proposed in U.S. Ser. No. 147,866 (filed May 8, 1980) cantilevers and diaphragms which are characterized by low density, high elasticity and high internal loss, the cantilevers and diaphragms being formed from a kneaded mixture comprising polyvinyl chloride, polyvinylidene chloride and flaky graphite powder. The proposed material has improved physical properties which are not found in prior art materials. In various application of the previously proposed material, the inventors encountered a problem that it is insufficient in temperature resistance. Elements made of this material tend to be deformed particularly when used in automobile audio sets which may be exposed to the summer sun or possibly used in the tropics.